500mm lens

I'm looking at two lenses on ebay, sold new, but haven't heard of these brands before, so I'm wondering if anyone has any experience with these brands and knows which is better, or if they are both junk. the first is a Rokinon f/8 and the second is a Opteka f/8.

This type of long focus lens is not all that bad....not fantastic, but not that bad actually. I own one, a Quantaray, which looks a lot like the Rokinon. Rokinon is an older cheap brand, Opteka is a newer cheap brand. I think the majority of these are made by two or three factories world-wide,and are labeled with many different store brands across the various regions of the world. These lenses are long, and light in weight, and need steadying, like a tripod or monopod, for best results. The optical formula and manufacturing process for these T-mount lenses has remained the same for 30 years or so. The quality is not as bad as you might think, and the price of around a hundred bucks is about right. They're good during the brighter weather months, and also now that Higher ISO performance has become so good, the f/8 max aperture is not the liability that it was years ago.